Heretofore others have used a shiftable clutching idler pulley belt drive, such as shown in U.S. Pat. No. 4,058,957, for establishing and disestablishing drive (transmission of power) between a drive pulley and a driven pulley. In using this type drive for the unloading auger of a combine, excessive start-up torque may be experienced resulting to either unsatisfactory life of components in the unloading drive train and unloading mechanism or the need to provide heavier duty components than would otherwise be required. The present invention proposes use of a dampener to slow the tensioning engagement of the clutching belt idler thereby limiting start-up torque. Others have heretofore suggested the use of a dampener in connection with a nonclutching belt idler, such as shown in U.S. Pat. No. 3,483,688.